Referring to FIGS. 1 and 2, a conventional screw driving gun 1 is shown to be adapted for use with a screw feed belt 140 that has a belt body 141 and a plurality of screws 142 retained on the belt body 141, and includes a gun housing 11, a tubular barrel 12, a tubular slider 14, a screw driving shaft 13, and a positioning member 15.
As illustrated, the tubular barrel 12 has a first circumferential wall 120 with a rear end 121 mounted on the gun housing 11, and an opposite front end 122. The first circumferential wall 120 defines a chamber 120C in a longitudinal direction. The tubular slider 14 has a second circumferential wall 144 with a rear portion 145 that is coupled slidably to the front end 122 of the barrel 12 so as to be slidable relative thereto in the longitudinal direction, and a front portion 146 that extends forwardly of the barrel 12. The front portion 146 of the slider 14 is formed with two opposing slots 147 that extend in the longitudinal direction and that are adapted for passage of the belt body 141 therethrough in order to register a selected one of the screws 142 with the chamber 120C of the barrel 12. The screw driving shaft 13 has a driven end 131 and a turning bit 132 opposite to the driven end 131. The screw driving shaft 13 is accommodated in the chamber 120C of the barrel 12 such that the turning bit 132 is extendible into the tubular slider 14. The screw driving shaft 13 is rotatable axially such that the turning bit 132 is adapted to drive rotatably the selected one of the screws 142. A drive unit (not visible) is mounted in the gun housing 11, and is coupled to the driven end 131 of the screw driving shaft 13 so as to drive rotatably the screw driving shaft 13. The positioning member 15 is secured to the front portion 146 of the tubular slider 14 for abutting against surface 170 of a work piece 17 that rests on a wall structure 18 so that the work piece 17 can be fastened on the wall structure 18 when the selected one of the screws 142 is driven and rotated by the turning bit 132 upon operation of the driving unit.
A disadvantage of the conventional screw driving gun 1 resides in that, in case the selected screw 142 is of a relative long length in the longitudinal direction, the belt body 141 is unable to maintain the orientation of the screw 142 in the longitudinal direction. Thus, deviation of the screw 142 relative to the longitudinal direction (shown in dotted lines in FIG. 2) will occur during the driving operation of the screw 142.